This article reviews some of the phenomena associated with tissue expansion that are amenable to study with 3D imaging and presents selected cases from the literature where the technology has been used to answer clinical questions and plan procedures. The authors discuss implant selection, remodeling, contraction, and 3D analysis. Future directions and limitations of the use of this technology in the head and neck are also described.
Three-dimensional imaging technology has only recently been described in the literature as a means to plan and better understand tissue expansion. This application is a logical use of the technology as the volume changes achieved with tissue expansion are controlled and often dramatic. This article reviews some of the phenomena associated with tissue expansion that are amenable to study with 3-dimensional imaging and reviews selected cases from the literature where the technology has been used to answer clinical questions and plan procedures. The future directions and limitations of the use of this technology in the head and neck will also be described.
Tissue expansion
Tissue expansion in a form near its modern evolution was first described as a means of head and neck reconstruction in 1957, and it has been proven a safe and effective means of reconstructing many defects in the head and neck. Although expanded tissue undergoes histologic changes, it provides a better color and texture match for many areas of the head and neck than tissue obtained from distant donor sites. Important changes related to tissue expansion include decreased density of hair follicles, increased vasculariity of the tissue, and the formation of a fibrous capsule around the expander.
Implant selection
Various tissue expanders are available commercially. The choice of implant is dependent upon the surgeon’s assessment of the defect to be reconstructed. Rectangular implants provide the greatest increase in surface area for the volume added, and oval implants have been shown to give a greater increase in surface area with a lower amount of pressure as compared with round implants. A greater surface area of tissue is obtained from a single oval tissue expander than 2 spherical expanders with a combined volume equal to the oval expander; however, multiple expanders are frequently used in the head and neck because of the complex nature of the anatomy. Overfilling expanders is a safe practice but increases the risk of leak at the injection port.
An accurate assessment of the size of the defect and the amount of skin required to reconstruct the defect is critical to implant selection. This is often based upon 2-dimensional measurements of the defect and adjacent skin. Specifically within the head and neck, linear measurements between points of static bony anatomy (ie, the nasion, angle of mandible, and midpoint of the clavicle) on the side of the defect may be compared with the contralateral normal side in determining the amount of skin required for a given reconstruction. Two-dimensional measurements of complex 3-dimensional defects can be misleading and often underestimate the surface area that will be required to fill a given defect.
Implant selection
Various tissue expanders are available commercially. The choice of implant is dependent upon the surgeon’s assessment of the defect to be reconstructed. Rectangular implants provide the greatest increase in surface area for the volume added, and oval implants have been shown to give a greater increase in surface area with a lower amount of pressure as compared with round implants. A greater surface area of tissue is obtained from a single oval tissue expander than 2 spherical expanders with a combined volume equal to the oval expander; however, multiple expanders are frequently used in the head and neck because of the complex nature of the anatomy. Overfilling expanders is a safe practice but increases the risk of leak at the injection port.
An accurate assessment of the size of the defect and the amount of skin required to reconstruct the defect is critical to implant selection. This is often based upon 2-dimensional measurements of the defect and adjacent skin. Specifically within the head and neck, linear measurements between points of static bony anatomy (ie, the nasion, angle of mandible, and midpoint of the clavicle) on the side of the defect may be compared with the contralateral normal side in determining the amount of skin required for a given reconstruction. Two-dimensional measurements of complex 3-dimensional defects can be misleading and often underestimate the surface area that will be required to fill a given defect.
Posterior expansion volume and bony remodeling
Tissue expanders can cause significant changes to the tissues underlying the implant that cannot be appreciated while the implant is in place. This phenomenon has been described as posterior expansion volume by Tepper and colleagues as it relates to breast reconstruction. The expander remodels the chest wall; thus some of the volume injected into the expander does not contribute to an increased surface area of skin available for the reconstruction. In this situation, there is a discrepancy between the volume change measured and the volume injected. This phenomenon is seen in the head and neck as well; expanders cause bony remodeling of the calvarium, with bone resorption in the center of the implant and reactive bone formation at the periphery.
Contraction
Once a tissue expander is removed, significant contraction of the expanded tissue is noted in the ensuing weeks and months. Some surgeons will remove all or part of the capsule around the expander, with the thought that the capsule with its increased density of fibroblasts is contributing to this phenomenon. Three-dimensional imaging has proven to be useful in analyzing contraction; a 20% decrease in expanded volume was noted over the 12 months subsequent to reconstruction of a patient with hemifacial microsomia using 3-dimensional photogrammetry.
Three-dimensional analysis
Several means of obtaining 3-dimensional surface images are presently available and are discussed more extensively elsewhere in this issue. Computed tomography (CT)-assisted 3-dimensional imaging generates a 3-dimensional surface image by superimposing photographs onto the surface generated by a CT scan, which is time-consuming and requires radiation exposure.
Three-dimensional laser scanners have been in use for some time and use a beam or stripe of laser light to capture multiple data points in space and generate a 3-dimensional image. Scanners are becoming faster and more portable. Stereophotogrammetry uses two or more cameras of a known focal length at different angles to the subject. The computer is able to generate a 3-dimensional rendering of the subject to within a millimeter. The Canfield VECTRA M3 3-D (Canfield Imaging Systems, A Division of Canfield Scientific Inc, Fairfield, ND, USA) camera and accompanying Mirror software were used to analyze data for the case presented in this article.
Three-dimensional analysis of tissue expanders
Reconstructive surgeons have begun to adopt 3-dimensional surface analysis of tissue expansion over the past decade. Initial reports analyzing cleft patients were among the first in using 3-dimensional facial imaging to understand a specific clinical entity and demonstrated the promise that this modality holds for improved understanding of complex facial structures.
Tissue expansion is a logical use for 3-dimensional imaging in that it allows surgeons to follow serial injections of a known volume and observe the effects on surface area over time.
Ying and colleagues first described the use of 3-dimensional analysis of tissue expansion using a laser scanner in a burn patient. Images were taken preoperatively to compare the normal side with the side to be reconstructed, and the difference in surface area was calculated to determine the area of expanded tissue that would be necessary for the repair. This calculation agreed closely with the actual measured size of the cheek defect. Subsequent imaging was performed on postoperative day 12 showing a 44% reduction in the surface area of the flap.
Tepper and colleauges described the use of 3-dimensional analysis of tissue expanders in 12 patients undergoing unilateral breast reconstruction. In the course of their study they used a 3-dimensional laser scanner to analyze patients before mastectomy, during tissue expansion, and postoperatively. The images were used to guide expansion volume, implant selection, and contralateral augmentation or reduction procedures. Overall they found improved breast symmetry when comparing pre- and post-reconstructive photographs. They also noted a discrepancy between injected and observed volume, which they attributed to remodeling of the chest wall and termed posterior expansion volume.
Jayaratne and colleagues described the use of 3-dimensional photogrammetry to determine the volume needed in the reconstruction of a patient with hemifacial microsomia by measuring the difference in volume between the 2 sides to be 16 cm 3 . A tissue expander was placed over the mandible, and serial expansions were performed until the expander had increased the volume to twice the required volume to allow for contraction. The expander was removed; a scapula free flap was used to correct the bony deficiency, and then serial 3-dimensional photographs were taken, showing that the majority of contraction occurred over the first 3 months. However, over the course of a year, 20% of the total volume gained by expansion was lost. This report was the first in using 3-dimensional photogrammetry to analyze tissue expanders in the head and neck.
Case Presentation
The Canfield VECTRA 3-D camera (Canfield Imaging Systems, A Division of Canfield Scientific Inc, Fairfield, ND, USA) was used to take photos during and after expansion in a patient undergoing an expanded paramedian forehead flap for reconstruction of a post-traumatic nasal defect. This case highlights some of the important uses, limitations, and questions that can be answered using this technology.
The patient was a young male who sustained severe facial injuries including a total nasal avulsion with soft tissue loss involving the upper lip. He had undergone multiple reconstructive procedures including a prior nasal reconstruction with a paramedian forehead flap. This reconstruction was complicated by a postoperative infection that caused loss of the structural grafts and partial loss of the paramedian forehead flap ( Fig. 1 ). Due to the scarring from the prior procedure and the large quantity of tissue required for coverage, reconstruction using an expanded paramedian forehead flap was planned.
